The mitochondrial regulation of smooth muscle cell proliferation in type 2 diabetes

Background: Type 2 diabetes (T2D) is associated with a strongly increased risk for restenosis after angioplasty driven by proliferation of vascular smooth muscle cells (VSMCs). Here, we sought to determine whether and how mitochondrial dysfunction in T2D drives VSMC proliferation with a focus on ROS and intracellular [Ca ²⁺ ] that both drive cell proliferation, occur in T2D and are regulated by mitochondrial activity.

Methods: Using a diet-induced mouse model of T2D, the inhibition of the mitochondrial Ca ²⁺ /calmodulin-dependent kinase II (mtCaMKII), a regulator of Ca ²⁺ entry via the mitochondrial Ca ²⁺ uniporter selectively in VSMCs, we performed in vivo phenotyping after mechanical injury and established the mechanisms of excessive proliferation in cultured VSMCs.

Results: In T2D, the inhibition of mtCaMKII reduced both neointima formation after mechanical injury and the proliferation of cultured VSMCs. VSMCs from T2D mice displayed accelerated proliferation, reduced mitochondrial Ca ²⁺ entry and membrane potential with elevated baseline [Ca ²⁺ ] _cyto compared to cells from normoglycemic mice. Accelerated proliferation after PDGF treatment was driven by activation of Erk1/2 and its upstream regulators. Hyperactivation of Erk1/2 was Ca ²⁺ -dependent rather than mitochondrial ROS-driven Ca ²⁺ -dependent and included the activation of CaMKII in the cytosol. The inhibition of mtCaMKII exaggerated the Ca ²⁺ imbalance by lowering mitochondrial Ca ²⁺ entry and increasing baseline [Ca ²⁺ ] _cyto , further enhancing baseline Erk1/2 activation. With inhibition of mtCaMKII, PDGF treatment had no additional effect on cell proliferation. Inhibition of activated CaMKII in the cytosol decreased excessive Erk1/2 activation and reduced VSMC proliferation.

Conclusions: Collectively, our results provide evidence for the molecular mechanisms of enhanced VSMC proliferation after mechanical injury by mitochondrial Ca ²⁺ entry in T2D.